The invention relates to a three-way 
NOx, CO and HC removing catalyst used in a 
marine engine, and a preparation method thereof. The catalyst takes 
cerium-
tin-
tungsten composite oxide as an 
active component, takes one or more oxides of 
cobalt, ferrum, 
nickel, 
copper, 
lanthanum, 
molybdenum, 
manganese, 
zirconium, silver and 
yttrium as a 
promoter, and takes AlSiTi 
composite oxide as a carrier. A saturated 
active component solution, a saturated 
cobalt promoter ionic solution, strong acid 
alumina gel, 
diaspore, clayey, 
titanium dioxide and an organic forming agent are stirred uniformly, mixed, aged and extruded for formation, and the integral type catalyst is obtained through 
drying and 
roasting. According to the invention, the catalyst has high 
NOx removing efficiency, the active temperature window is wide, and the CO and HC removing efficiency is high in a low-temperature collaborated catalyzing manner. According to the catalyst, as the components of the catalyst are nontoxic and environmental-friendly, the catalyst has the advantages that the 
mechanical strength is high, the vibration resistance as well as the 
heat resistance is excellent, the preparation technology is simple, and the cost is low. The three-way 
NOx, CO and HC removing catalyst is applicable to treatment of NOx, CO and HC in 
tail gas of a marine 
diesel engine, and is also applicable to treatment to 
tail gas of other moving sources diesel engines such as automobiles.